Heating and cooling systems often contain a variety of heat exchangers for heating and cooling of liquids and gases, e.g. water, steam and/or air. In general, the various types of heat exchangers may be broken down into three main categories: Shell and Tube Heat Exchangers, Plate and Frame Heat Exchangers, and Air Coils.
Shell and Tube Heat Exchangers are the most common type of heat exchanger found in the background art. Normally, a bundle(s) of tubes is (are) enclosed within an outer shell. The tubes are joined to a tubesheet that prevents a fluid contained within the tube-side of the heat exchanger from becoming contaminated with a fluid contained in the shell side of the heat exchanger. Heat transfer is typically conducted across the tube walls separating the two fluids.
Baffle plates are commonly used to hold the tube bundles in their desired positions. The baffle plates will also serve the function of directing the shell side fluid across the exterior of the tube walls in order to achieve efficient heat transfer. The fluid passing within the tubes may make several passes through the heat exchanger in a common U-type arrangement involving U-shaped tube bundles and end plates/headers, or may make only a single pass through the heat exchanger.
The use of baffle plates on the shell side of heat exchangers has been in existence for many years. These baffle plate arrangements may utilize circular plates fitted within the shell enclosure that additionally have holes cut within the surface of the plate to secure the tubes that pass therethrough.
FIG. 1 is a side elevation view of a heat exchanger according to the background art. FIG. 2 is an enlarged, end view of a baffle plate for the heat exchanger shown in FIG. 1. A shell and tube heat exchanger 1 incorporating a U-shaped tube bundle 20 is generally shown in FIG. 1. A plurality of tubes 21 is provided connecting a tube side fluid flow through a tube side fluid inlet 22 and a tube side fluid outlet 23. A shell 10 having a shell side fluid inlet 11 and shell side fluid outlet 12 encloses the tube bundle therein. A baffle plate 30 having a plurality of tube holes 35 cut therein is shown in more detail in FIG. 2.
The baffle arrangement shown in FIG. 1 achieves a series of four, flow diversions (changes in flow direction) that essentially imparts a sinusoidal flow stream to the shell side fluid. This is achieved through the use of four semi-circular baffle plates 30 that extend only partially through the width of the shell 10. The baffle plates 30 move fluid in a sinusoidal (cross-sectional) manner on the shell side of the heat exchanger and thereby achieve longer contact time for the shell side fluid with the fluid contained within the tubes.
Depending on the arrangement desired in the heat exchanger, the resulting shell side fluid flow can be either parallel flow (in parallel with and in the same flow direction of tube side flows), counterflow (in parallel with but counter to the flow direction of tube side flows), or cross-flow (tangential or normal to the direction of tube side flows). As seen in FIG. 1, the fluid within the tube side of the heat exchanger 1 enters at the tube side fluid inlet 22 and exits at the tube side fluid outlet 23, thereby making two passes through the heat exchanger 1.
A first tube side flow path is defined by and extends from, as viewed from left to right in FIG. 1, the tube side fluid inlet 22 to a tube side header 24. A second tube side flow path extends from the tube side header 24 to the tube side fluid outlet 23. Therefore, fluid flow on the shell side of the heat exchanger flowing from left to right in FIG. 1 flows in the same direction (parallel flow) as fluid in the first tube side flow path and counter (counterflow) to the flow direction in the second tube side flow path. However, the baffle plates 30 impart a partial cross-flow of the shell side flow path with respect to the tube side flows.
One shell and tube type heat exchanger is currently used for the cooling of CVD/CVI furnaces. This type of heat exchanger may have multiple banks of heat exchangers with several tube side fluid inlets and tube side fluid outlets. The heat exchanger may also have a turbine installed in the same heat exchanger housing that draws upon fluid leaving the shell side fluid outlet of the heat exchanger. The heat exchanger may even be separated from the turbine inlet using a circular baffle plate, e.g. having a hole in the center of the plate for permitting controlled flow to the turbine inlet.
However, this type of arrangement does not permit isolation or control of the individual banks of heat exchangers when multiple tube banks are utilized in the heat exchanger.